1. Field of the Invention
The present invention relates to a method of filling the inner region of a graphic with traces of an imaging spot having a predetermined size on an image plane.
2. Description of Background Art
In order to automatically produce a master film used for manufacturing a printed circuit board, a photoplotter is used in which a light spot is moved along a designated path on X-Y plane so as to expose a photosensitive film according to a predetermined pattern. The data indicating the position and the shape of the pattern may be prepared with a computer aided design device (CAD). The pattern is usually expressed by border lines of a closed geometric shape such as a polygon, a circle or the like, referred to herein as a "graphic". Therefore, the data indicating the pattern must be converted into "a filling data" expressing paths of the light spot in the case where the inner region of the graphic should be filled with traces of the light spot corresponding to the paths. The data conversion is conducted in a prior art device through a semimanual processing in which an operator observes the graphic and serially designates the paths with a digitizer. The prior art has one disadvantage in that it requires a substantially large time for conducting the data conversion. Another disadvantage is that the designated paths sometimes deviate from those for exposure at a high efficiency because the semimanual processing depends on the skill of the operator.
An improvement for the data conversion has been developed, but it is not sufficient for aforementioned the disadvantages. For example, suppose the case where parallel vectors are generated for designating the paths along which the inner region of a graphic is scanned with the light spot. If the graphic has a concavity, the parallel vectors are increased in number since vectors are interrupted by the mentioned concavity. Furthermore, the respective points on the border lines of the graphic must be sorted along two directions, one of which is for serially generating the vectors and the other is for distinguishing the inner region of the graphic from the outer region thereof in order to automatically detect the inner region to be filled. As a result, such an improvement also requires a long time for data conversion.